FIELD OF THE INVENTION
This invention relates to a transparent fire-screening glazing panel having at least one solid intumescent layer comprising a hydrated alkali metal silicate and at least one sheet of glazing material. The invention includes a process of manufacturing such a panel.
Layers of intumescent material are often associated with sheets of glazing material to form fire-screening panels. For example such a layer may be sandwiched between two glass sheets. A very important application of such panels is as transparent closures of viewing apertures of rooms or other enclosures where there may be a risk of fire.
It is extremely important that the intumescent material layer of such a panel should be transparent and that it should maintain high transparency and acceptable optical properties until it starts to become tumid on the outbreak of fire.
One problem which is associated with the use of hydrated silicate layers as intumescent material is the rapid aging of the material over the course of time. This aging is apparent as a reduction in the transparency of the hydrated intumescent material which in turn reduces the transparency of the panel. Such a deterioration in the properties of a panel will clearly be prejudicial to its use.
The problem of reduced transparency on aging of a fire-screening panel has been known for many years, and various attempts have been made to solve this problem. A major cause of the reduction in transparency has been the appearance of micro-bubbles in or at the surface of the layer, and it is known to make up the solution of the hydrated alkali metal silicate using water which has been degassed, and to take care when mixing the solution not to agitate the solution to such an extent that air or other gas becomes redissolved so that it can reappear as the dried layer ages. While this gives an improvement in the aging properties of the panel, it is not entirely satisfactory. While some known fire-screening panels may have suitable aging properties for use in the interior of a building, we have found that their aging properties are not good enough if they are to be used in circumstances where they are exposed to mild heat, for example due to direct sunlight. This aspect of the problem is manifested in the appearance of haze in the intumescent layer, and it is an object of the present invention to provide a fire-screening panel of the kind referred to in which the appearance of haze is delayed.